Solution Synthesis of Ternary Solid-State Electrolytes for Sodium-Ion Batteries

Lithium-ion Batteries (LIBs) are the current standard for rechargeable batteries. However, the growing demand predicted by increasing electric vehicle and grid applications has raised concerns due to the scarcity of lithium resources. Sodium analogs are attractive for renewable electricity storage due to high abundance, lower cost, and reduced environmental impact relative to their lithium counterparts. Na-based batteries employing solid-state electrolytes (SSEs) such as sulfides are being explored to improve reliability and performance. These materials are typically synthesized through high temperature solid-state reactions conducted in quartz ampoules followed by ball-milling, which is very energy and time-intensive and not amenable to scale-up. In this work, we describe simple and cost-effective routes for the synthesis of sodium thioantimonate (Na₃SbS₄), an attractive SSE with high ionic conductivity and stability in protic solvents. First, we demonstrate the synthesis of the Sb₂S₃ precursor via thermodynamically favorable metathesis between Na₂S and SbCl₃. This solution-based approach is further extended by coupling the resulting Sb₂S₃ with Na₂S for the synthesis of Na₃SbS₄. We demonstrate that ethanol is a superior solvent to water for the synthesis of Na₃SbS₄ with respect to yield, morphology, and performance. Amorphous Sb₂S₃ synthesized from low-temperature metathesis reaction produced highly crystalline Na₃SbS₄ with a room temperature Na⁺ conductivity of 0.52 mS/cm and low activation energy, comparable to leading values reported in the literature. Alternatively, we describe the single-step synthesis of Na₃SbS₄with similar performance by directly utilizing Na₂S and SbCl₃ as precursors. This approach simplifies the current multi-step synthetic route that is accompanied by extensive raw materials loss and reduction in overall reaction yield.